It is known that nickel-based superalloys have been employed in high performance environments. Such alloys have been used in machinery, such as gas turbine engines, where they have retained high strength and other desirable physical properties at elevated temperatures of up to 650° C. (1200° F.). An example of such an alloy may be found in U.S. Pat. No. 3,519,503, the disclosure of which is incorporated herein by reference.
The operation of a gas turbine engine is known. Air compressed by a shaft-mounted compressor disk can be mixed with fuel. The ignited mixture can result in a hot exhaust gas which can power the compressor and drive the engine. A turbine disk may be mounted to a drive shaft. Turbine blades can extend from the periphery of the turbine disk. The compressor disk can be mounted to a shaft which is driven by the turbine shaft.
The turbine disks which support the turbine blades may rotate at high speeds in an elevated temperature environment. These turbine disks may encounter different operating conditions radially from the center or hub portion to the exterior or rim portion. For example, the turbine blades are exposed to high temperature combustion gases which rotate the turbine. The turbine blades may transfer heat to the rim portion or section of the disk. As a result, the temperatures in the rim portion may be higher than those in the hub or bore portion. Furthermore, the stress conditions may also vary across the turbine disk.
Aerospace and space propulsion may require materials capable of peak temperatures as high as 760–815° C. (1400–1500° F.). Other propulsion systems, such as commercial aircraft engines in cruise conditions, may operate at moderately elevated temperatures for long periods of time. There is needed an alloy capable of providing improved physical and mechanical properties at these high temperatures and/or at these elevated temperature time periods.
Previous attempts to modify alloy chemistry for improved strength and time-dependent properties at high temperatures included increasing the content of strengthening gamma prime precipitates, and increasing the inherent strength and time-dependent properties of the gamma prime and gamma phases. The content of gamma prime precipitates can be increased by increasing the amounts of certain elements which stabilize and preferentially reside in the gamma prime phase precipitates. The inherent strength and time-dependent properties of the gamma prime phase precipitates can be increased by increasing the amounts of certain refractory elements to take the place of Al atoms in the L12 crystal lattice of gamma prime. The inherent strength and time-dependent properties of the gamma matrix phase can be increased by providing more refractory elements to take the place of Ni atoms in the FCC crystal lattice. However, these previous approaches have resulted in alloys with disadvantages and/or limitations. For example, problems still remain for the “Supersolvus” class of alloys optimized with coarse grain microstructures for mechanical properties at high temperatures in the range of 704–815° C., typified in U.S. Pat. No. 5,143,563 (the disclosure of which is incorporated herein by reference) and U.S. Pat. No. 5,662,749 (the disclosure of which is incorporated herein by reference). These alloys remain difficult to heat treat, require high solution temperatures often above 1160° C. for coarse grain size, and/or are difficult to quench without forming cracks. Even with coarse grain size, the alloys tend to have insufficient creep, tensile, and fatigue properties at temperatures approaching 815° C. than required. For the alternative “Subsolvus” class of alloys, typified in U.S. Pat. No. 3,519,503 (the disclosure of which is incorporated herein by reference) and U.S. Pat. No. 5,104,614 (the disclosure of which is incorporated herein by reference), which are heat treated at lower solution temperatures and optimized with fine grain microstructures for mechanical properties up to 704° C., problems also still remain. They do not have sufficient strength, creep, and fatigue properties at temperatures up to 815° C. The Subsolvus alloys also do not respond favorably to alternative coarse grain heat treatments, due in part to their high gamma prime solvus temperatures. Advanced dual microstructure heat treatments were thereby difficult to apply successfully to either the Supersolvus or Subsolvus class alloys. Additionally, while advanced dual microstructure heat treatments could be applied to a more recent “Balanced subsolvus/supersolvus” class of alloys, typified in European Patent Application EP 1 195 446 A1 (the disclosure of which is incorporated herein by reference), these alloys also had insufficient tensile and creep properties at the temperatures required.
Thus, there exists a need for a high temperature, high versatility alloy capable of use in advanced propulsion applications. In particular there is a need for a disk superalloy having higher inherent strength and creep resistance near the peak rim temperatures, maintained dwell crack growth resistance at lower temperatures, and sufficient phase stability at these temperatures for expected total service lives approaching several thousands of hours.